1. Field of the Invention
The present invention relates to a lifting column, preferably for height-adjustable tables, the lifting column including at least two relative to each other telescopically arranged members and at least one slider arranged between the two members, the slider being secured to one of the two members. Further, the invention relates to a table furnished with a lifting column of the type described above.
2. The Prior Art
The focus on working environment in recent years has resulted in a wish for free height-adjustment of also common work tables, such as desks. In that connection, lifting columns especially for tables have been developed during the past decade which allows a person to choose freely whether he wishes to sit or stand at the table. This development has caused the price for the height-adjustment to become a determining factor. According to European standard EN 527 the table should be adjustable from a height of 60 cm to 120 cm, but some standards prescribes a higher height, e.g., the Dutch standard NEN 2449, which prescribes an interval from 62 cm to 128 cm. The standing height of the desk makes special demands on the stability of the lifting columns.
The lifting columns are usually made from steel tubes or extruded aluminum tubes cut into desired lengths. Between the individual members the lifting column is furnished with sliders of plastic in the shape of bushings and/or separate bricks, just as sliders in the shape of axially running lists are also known. In some cases ball guides are also used between the members, cf. e.g., WO 97/47217 A1 Herbert Grüttner GmbH & Co KG, which is being practiced by Linak A/S, Denmark, in the lifting column, DL1. On the whole, with regard to the price, only sliders of solid plastic are used.
Generally seen, the tubes are subject to two innate disadvantages—the first being a relatively large dimensional tolerance, which causes relatively large variations in the gap between the members. This further results in that a relatively large play may occur between the members. The play causes the table to appear unstable, which from a user's point of view is unacceptable. A processing of the tubes in order to reduce the dimensional tolerances would result in the lifting columns being unacceptably expensive.
The other disadvantage is that the tubes during the manufacturing process may be twisted about their longitudinal axis. For a tube having, e.g., a square cross section this would result in the cross section, being twisted out off angle, which would cause the gap between the two members to become non-uniform, unless they by chance have the same angle of twist. The gap will not only be non-uniform in its width, but will also vary depending on how much the two members have been twisted relative to each other. It becomes even more troublesome if the two members have been twisted in opposite directions.
To counter the play, adjustable sliders which may be fitted to the present width of the gap have been developed, cf. e.g. EP 1 250 866 A1 Assenburg BV, EP 1 004 784 A1 Magnetic Elektromotoren AG and DE 298 12 762 U1 Phoenix Mecano Komponenten AG, which are all based on sliding wedge-shaped elements in the sliders. Another solution is disclosed in DK-171 903 B1 Linak A/S having adjusting screws for pressing the slider into engagement. In any case the mounting becomes difficult and time-consuming.
WO 02/063996 A1, Rol Egonomic AB discloses a solution for lifting columns having a circular cross section, where sliders in the shape of open rings are placed in countersunk grooves in the members. The solution only takes a situation into account where the slider is larger than the gap between the members. In this situation the slider retracts and adapts to the gap. The solution does not allow for the opposite situation where the gap is wider than the slider. Furthermore, an internal countersinking of grooves in the members is a relatively expensive process.
EP 1 479 963 A2 Heinrich J Kesseböhmer KG discloses a solution with a slider consisting of a hard and a flexible layer, where the flexible layer is intended for compensating for manufacturing and dimensional tolerances. The idea is thus to harden the flexible layer after the mounting. This is a demanding, uncertain and undoubtedly expensive process.
WO 03/047389 A1, Linak A/S discloses another solution where the slider which fits the gap between the members best is chosen from a range of sliders with various thickness where after a local deformation across from the slider is carried out in order to equalize the dimensioning tolerances. Thus, a highly stable lifting column is achieved but the mounting is obvious difficult and expensive, just as the tool for performing the local deformations is rather expensive.
The purpose of the invention is to provide a lifting column as stated in the introductory portion with a simplification of the mounting process of the sliders, which further ensures a stable lifting column.